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NATURE 



[July 12, 1917 



LETTERS TO THE EDITOR, 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature; No notice is 

 taken of anonymous communications.] 



Synchronous Signalling. 



The following- Board of Trade notice to mariners, 

 recently issued, is one of exceptional interest and im- 

 portance; for, thanks to American initiative, we find 

 here for the first time a practical application of the 

 principles of synchronous signalling. 



"New York Harbour Approaches.— FtVe Island 

 LJV. Radio Dist. Determining Apparatus Installed. 

 — The attention of all ships nav. the approaches 

 to New York Harb. is invited to the recent installa- 

 tion on Fire Island L/V. of a combined radio and sub- 

 merged sound sig. transmitter which determines the 

 receiving ship's distance from the L/V. (Call letters 

 NLS. ; station, 40° 28' 40" N., 73" 11' 26^ W.) 



"This apparatus will be in operation during fog, 

 mist, rain, or falling snow. The range of this appa- 

 ratus is limited to the receiving range of the sub- 

 marine bell receiving equipment employed on ship- 

 board, and in all practical cases this is within six or 

 seven miles. The submarine bell strikes six strokes, 

 pause, then eight strokes once every 38 sec. Begin- 

 ning shortly after the first stroke of the *6' sub- 

 marine character, about ^ sec, the ship emits a series 

 of radio sigs. In order to determine the dist. of a 

 ship from the L/V. it is necessary to count each of 

 these radio dots until the first stroke of the six sub- 

 marine sigs. is received. The number of dots thus 

 determined gives the dist. in half sea miles from the 

 L/V. Example : — (a) Eleven radio dots are received 

 before the first stroke of the bell; the dist. is 11/2, or 

 5^ miles, (b) Four radio dots are received, the first 

 submarine bell sig. appearing midway between the 

 fourth and fifth radio sig. ; the total number of radio 

 sigs. received is 4^, and the dist. is 4J divided by 2, 

 or 2j miles. The most convenient method of receiv- 

 ing these sigs. is to have one receiver connected to 

 radio and the other receiver connected to submarine 

 bell detector, thereby connecting one ear to radio 

 sigs. and the other to submarine sigs. These sigs. 

 will also be furnished in clear weather when re- 

 quested to do so by radio. It is requested that all 

 passing vessels equipped with submarine sig. receiv- 

 ing apparatus familiarise themselves with this appara- 

 tus and report success obtained to the Hydrographic 

 Office. Wave length used is 600 metres. Watches 

 are stood as follows : — (i) Continuously during thick 

 weather. (2) During clear weather, first 15 min. of 

 every hour from 8 a.m. to 9.15 p.m. Although this 

 station has proved accurate on test, the apparatus is 

 in an exper. stage, and too much reliance should not 

 be placed on it until its worth has been proved under 

 service conditions." 



It will be understood that the particular mode of 

 applying synchronous signals herein described enables 

 the mariner to dispense with the use of stop-watch or 

 chronometer. The ordering of the faster-travelling 

 signals is such as to supply the place of a timepiece. 

 If a wireless and submarine signal be started together, 

 the latter lags 1-2 sec. for each mTle travelled, or for 

 each half mile the lag is 06 sec. Hence if the instan- 

 taneous signal is repeated every 06 sec, the first 

 of these being emitted o-6 sec. after the first sub- 

 marine signal, the mariner at half mile distance from 



NO. 2489, VOL. 99] 



the shore station gets both initial signals together^ 

 At one sea mile he gets the first submarine signal 

 along with the second radio dot ; at one and a half sea 

 miles the third radio dot coincides with the first sub- 

 marine bell stroke. Hence the rule : Divide by 2 tO' 

 find the distance in sea miles. If the mariner is 

 closer than half a mile the submarine signal comes 

 in first. It is, perhaps, open to question if this is 

 better than the arrangement of starting the signals 

 at the same instant. In the latter case the mariner 

 counts up the radio dots until the submarine signal is 

 heard, subtracts i, and divides by 2. In this ordering 

 he always hears the radio signal first. 



It is to be hoped that this will be a successful inau- 

 guration of a reform in maritime signalling. Our 

 signalling stations are not nearly so valuable as they 

 would be if synchronous signalling was made more 

 general. In many cases the more important appa- 

 ratus required is already installed. It must be borne 

 in mind that both light-flash and aerial sound signals 

 of abrupt character may be used in synchronous 

 signalling. 



The application of synchronous signalling to avoid- 

 ing collision at sea is perfectly simple, and the step 

 now taken should lead to its careful consideration and 

 trial. In this case a vessel. A, when overtaken by 

 thick weather, emits synchronous signals, say, every 

 two minutes. This would be automatically effected by 

 a clock-work contact maker. (The radio signals might 

 consist of eight or ten consecutive dots spaced o-6 sec. 

 apart.) Another ship, B, hearing these, not only 

 learns of the presence of A, but also gets her distance 

 at once. B is also signalling, so that like information 

 reaches A. Each ship now signals her course and 

 speed. This is a familiar operation between ship 

 station and shore station or between one ship station 

 and another, and takes only a few seconds. The 

 navigating officers on A and B then read on an instru- 

 ment of simple construction (i) the rate at which the 

 ships will be nearing one another, and (2) the mutual 

 bearings of the two ships — if collision is threatened. 

 And now after two minutes each officer, on receiving 

 the second synchronous signal of the other ship, is 

 able to say whether danger threatens him or not. For 

 if this second signal tells him that the ships have 

 approached each other by a certain distance during the 

 two minutes (a distance read directly on the "Collision- 

 Predictor .") there is danger of collision. If thedistance 

 covered is less than this (it cannot be erreater), there 

 is safety. The third synchronous signal may be used 

 to confirm the result. 



By this method, if the danger of permitting ships to- 

 sail in open waters unprovided with the requisite 

 equipment (both instrumental and personal) be avoided 

 by proper and stringent regulations, high speeds in 

 open ocean could with safety be maintained in any 

 weather. J. Joly. 



Trinity College, Dublin. 



Calculating Machines. 



May I make an appeal through your columns to 

 any men of science who have calculating machines 

 of any kind not in active use to communicate with 

 me? My laboratory has at present very heavy com- 

 puting work of an urgent character in hand for a 

 Government department. This keeps nine machines 

 running almost incessantly, and when any machine 

 gets out of order it is, in existing circumstances, 

 almost impossible to get it rapidly and effectively 

 repaired. Quite fancy prices are now being asked 

 often for completely worn^ut machines. If any one 

 of the readers of Nature has a machine in reason- 



